1. Field
The present disclosure generally relates to methods and apparatus for sensing the presence of a transmission signal in a wireless channel, and more particularly to spectrum sensing of a particular transmission signal type in the wireless channel.
2. Background
In particular wireless networks including cognitive radio technology operating according to IEEE standard 802.22, as an example, unlicensed wireless operation is permitted in unused television channels. In order to prevent operation in channels that are currently used by licensed wireless devices at a given time, user devices in such networks preferably need the ability to observe the spectrum and identify channels that are occupied by licensed users or other users. As an example, it is noted that the licensed users may be Advanced Television Systems Committee (ATSC) digital television transmissions, National Television Systems Committee (NTSC) analog television transmission or licensed wireless microphone transmissions. The process of observing the wireless spectrum and identifying occupied and unoccupied TV channels is referred to as “spectrum sensing.” This spectrum sensing capability is often one of the capabilities of cognitive radio devices in order to identify unused frequency bands in the RF spectrum that may be used by the devices.
Presently the Institute of Electrical and Electronics Engineers (IEEE) is developing a standard for unlicensed wireless networks (e.g., working group IEEE 802.22) that operate in the television bands. This standard will utilize cognitive radio techniques for sensing the presence of particular signals, such as wireless microphone signals, in order to identify unused TV channels, for example. It is noted that there are several possible licensed transmissions that may occupy a TV channel, such as analog TV, and Advanced Television Systems Committee (ATSC) digital TV, as well as professional wireless microphones.
Licensed wireless microphones operating in the television bands, in particular, are typically analog FM devices. The bandwidth of these devices is limited to less than 200 kHz, with a typical bandwidth being even narrower at approximately 100 kHz. Since these devices utilize FM modulation, the bandwidth of the transmission depends on the amplitude of the audio signal. Accordingly, it known that some manufacturers of wireless microphones add a high-frequency tone into the audio signal before modulation to assist intended receivers of that signal in identifying the wireless microphone transmission given the relatively narrow-band signal. This high-frequency tone is referred to as a “tone-key,” allows the receiver to squelch the audio signal when no signal is present.
Devices within the above-described systems may scan a frequency spectrum of the wireless channels in order to attempt to identify unused spectrum. Certain types of transmissions may not be accurately detected by merely scanning the frequency spectrum. With wireless microphones, in particular, because the volume of an attendant audio tone-key signal causes fluctuations in the bandwidth of the particular wireless microphone signal, frequency scanning may be difficult. As such, benefits may be realized by methods and apparatus with improved accuracy in detecting the presence of a particular transmission signal in a wireless channel.